A history of development of IT technology saw a transition from a stage that centers on computer technology and driven by the development of processors to a stage that centers on transmission technology. The transition promoted the development and popularity of computer network. The information of an increasing number of business activities become digitized, leading to an explosive increase in digitized information and a growing demand for storage techniques of the IT technology. New characteristics such as mentioned below have emerged in data storage applications:
(1) Data has become the most valuable asset. Losing data can bring inestimable and even destructive damages to a company.
(2) The total amount of data has increased explosively.
(3) Around-the-clock service has become the trend. 365×24 hour service becomes the norm in e-commerce and most network service applications, and requires existing data storage system to possess excellent high availability.
(4) Storage management and maintenance are required to be centralized, automatic, and intelligent.
(5) Storage technique needs to be platform independent.
Conventional storage system uses DAS (Direct Attached Storage), i.e., storing through a direct connection, which is also called SAS (Server-Attached Storage). In this approach, a storage device is directly connected to a server through a cable (usually a SCSI connecting cable). An I/O (input/output) request is sent to the storage device directly. This storing approach relies on the server, while the storage device is simply a pile of hardware without any storage operating system. Because of limitations for server bus technology, systems using DAS have poor expansibility. If the number of user connections increases, the server may become a performance bottleneck of the entire system because the following reasons.
(1) Bandwidth limitation of a computer. Although the development of computer technology has led to an increase in bus bandwidth of a computer, the increase still fails to keep up with bandwidth requirement of modern storage applications.
(2) Memory capacity limitation of a computer. As memory capacity of a computer is limited, if there are continuously large numbers of data access requests, the memory capacity of the computer will be saturated quickly, thus failing to process remaining requests for data transmission.
(3) Overhead for management of a file system may also increase data access time.
A large number of existing corporate applications rely heavily on database technology, and use centralized database server for centralized data storage. These applications are generally a single point and a performance bottleneck of the associated system. In addition to being costly and hard to expand, these corporate applications also have particular difficulties in concurrently processing a large amount of data online. Therefore, conventional approaches using centralized data storage and management are no longer able to satisfy rapidly growing demands.